AY201b, 4•16•13What goes on in “(Super)shells”?

(Effects of massive stars on the ISM.)

Recommended references Draine: Chapters 37, 38, 39

Shu: The Physics of Astrophysics, Volume II, Gas Dynamics, Chapter 20 (AG’s favorite)

20 cm VLA from MAGPIS (Helfand et al. 2006) & MIR from Spitzer GLIMPSE (see Churchwell et al.)3.6, 4.5, 8.0, 20cm (Luptonized, see Lupton et al. 2004)

image “height” is 1.6 degrees (e.g. 140 pc at 5 kpc)

radio SNR

warm dust cold dust

HII regions(+SNR)

Massive Star-Forming Regions

What Stars can do to the ISM (reminder from Day 1!)

Evolution of an HII Region in a Turbulent Medium

from S.J. Arthur 2007

back mid-plane front

80,000 yr

209,000 yr

black =105 cm-3

white = 10 cm-3

black = 0 Kwhite = 104 K

M17

Tasting “M17”...

Synthetic [OIII], H and [NII] emission-line image from a 5123 numerical simulation: Mellema, Henney, Arthur & Vàzquez-Semadeni 2009

A really big HII region...

IC 1396 in H

http://apod.nasa.gov/apod/image/1208/IC1396_demartin_1324.jpg

3 degrees across at 1 kpc

= 50 pc across

principal ionizing stars: HD 206267 triple system

05, 08, B1

“Supershells”

A really big HII region...

IC 1396 in H

http://apod.nasa.gov/apod/image/1208/IC1396_demartin_1324.jpg

3 degrees across at 1 kpc

= 50 pc across

principal ionizing stars: HD 206267 triple system

05, 08, B1

Patel et al. 1998, CO “super” shell

Extragalactic Contexts...(coming soon)

http://www.exp-astro.phys.ethz.ch/highlights/highlights_sept07.html

Upper panel radius RI of the ionization front versus time for expansion of an H II region into an initially uniform neutral cloud with n0 = 103 cm−3, for an ionizing source with Q0 = 1049 s−1. Dust absorption is neglected. For this example, the ionization front makes the transition from R-type to D-type at time tD ≈ 540 yr. Lower panel Velocity VIF of the ionization front, and velocity υi (relative to the star) of the gas just interior to the ionization front.

Figure 37.3 from Draine, Bruce T. (2010-12-20). Physics of the Interstellar and Intergalactic Medium (Princeton Series in Astrophysics) (Kindle Locations 9443-9448). Princeton University Press. Kindle Edition.

540

year

s

“However, when Vi falls below uR, the character of the expansion will suddenly change: a shock wave will now move ahead of the I-front, and will compress and accelerate the neutral gas so that the I-front is moving into gas that has been both compressed and set into motion. The I-front will now be weak D-type, but it will be advancing into neutral gas that is already moving radially outward as the result of the shock.”

100,

000

year

s

1 pc

10 pc

RS ~0.4 pcExpansion of HII Region in Uniform

Medium(no dust)

Definitions:I-front: ionizaton front, separating neutral & ionized material (e.g. at boundary of H emisision)

D-type I-front: I-front encounters gas that is pre-compressed by a shock (e.g. if pressure rise created by photdissociation/photoinoizaton boosting the number of free particles & raising temperature is enough to cause a shock)“strong D-type” very slow flow in the netural medium, approximate pressure equilibrium across the front (happens late in evolution of expanding HII region)“weak D-type” ionized gas at much lower density than neutral gas, flows away from I-front at close to the speed of sound (rocket effect; gradient accelerates ionized gas away from I=front)

R-type I-front: I-front that is not preceded by a shock“strong R-type” means only a small density change across the I-front, asympoting to zero change as front goes faster“weak R-type” ionized gas much denser than neutral gas, only happens if there is a large pressure gradient across the front, meaning the I-front is also a shock front (~doesn’t happen in astro situations b/c shock & I-front need to move at ~exactly same speed)

Draine Shu

Definitions:I-front: ionizaton front, separating neutral & ionized material (e.g. at boundary of H emisision)

D-type I-front: I-front encounters gas that is pre-compressed by a shock (e.g. if pressure rise created by photdissociation/photoinoizaton boosting the number of free particles & raising temperature is enough to cause a shock)“strong D-type” very slow flow in the netural medium, approximate pressure equilibrium across the front (happens late in evolution of expanding HII region)“weak D-type” ionized gas at much lower density than neutral gas, flows away from I-front at close to the speed of sound (rocket effect; gradient accelerates ionized gas away from I=front)

R-type I-front: I-front that is not preceded by a shock“strong R-type” means only a small density change across the I-front, asympoting to zero change as front goes faster“weak R-type” ionized gas much denser than neutral gas, only happens if there is a large pressure gradient across the front, meaning the I-front is also a shock front (~doesn’t happen in astro situations b/c shock & I-front need to move at ~exactly same speed)

Adding Dust...

Adding Magnetic Fields..

Krumholz et al. 2007